A particulate cGMP-stimulated PDE was purified from bovine brain cerebral cortex. Photolabelling of cGMP-stimulated PDEs from bovine brain or calf liver with [32P]cGMP, followed by proteolytic digestion with V8 protease and peptide mapping (Cleveland et al., J. Biol. Chem. 252: 1102, 1977), indicated that 32P was predominantly associated with peptide(s) of about 12-14 kDa, suggesting that cGMP binding sites might be located in conserved domains of different cGMP-stimulated PDEs. Partial amino acid sequences were determined for the photolabelled fragment and other peptides. On Western immunoblots, antibodies against a synthetic peptide with a sequence matching part of that of the photolabelled fragment cross-reacted with intact PDE and the photolabelled fragment. Deduced amino acid sequence from a partial cDNA clone (isolated from a Lambda Zap II bovine brain library screened with an oligonucleotide probe based on the amino acid sequence of another peptide), as well as the partial sequence of the photolabelled fragment, exhibited considerable identity with the putative cGMP-binding domain of a cardiac cGMP-stimulated PDE (Charbonneau et al., Proc. Natl. Acad. Sci. 87: 288, 1990). These results suggest that cGMP-stimulated PDEs will exhibit considerable homology in at least the cGMP-binding region.